The study of the nuclear replicating, double stranded DNA viruses (herpes, adeno and papova viruses) has yielded much information regarding the molecular biology of gene expression of both viruses and eucaryotes in general. We have extended these studies through the examination of several aspects of gene expression control of the late genes of the papova virus, Simian virus 40 (SV40). Specifically: 1. We have examined the mechanisms by which the SV40 early gene product, large T antigen, trans- activates the promoter for late gene expression, and we have defined elements within the late promoter which respond to trans- activation. Our data suggest that T antigen mediates the activation of the late promoter (and cellular promoters) indirectly through the utilization of a cellular trans-acting factor(s). Such abrogation of cellular trans-acting cellular phenotypic changes associated with viral disease and transformation. We propose to use several lines of investigation to further analyze the trans- activation mechanism and exactly delineate the elements of the late promoter. In addition, we will initiate experiments to identify cellular trans-acting factors which direct late promoter activation. 2. We have defined sequences of the 3'-slide of the hexanucleotide AAUAAA which effect efficiency of polyadenylation of the viral late RNAs. Our data indicate that there may be separable parts to this downstream signal element. We propose to carefully define these elements and their interrelatedness. Additionally, our data suggests that sequences on the 5'-side of the late AAUAAA affect the level of late transcripts, possibly by stabilizing the transcript. We propose to examine these sequences and determine their function. 3. We have examined the effect of the SV40 agnoprotein on the expression and intracellular localization of late viral gene products. We propose to continue these studies in order to better understand the phenomenon and determine the function(s) of the agnoprotein.